1. Field of the Invention
This invention relates generally to an electronic musical instrument and, more particularly, to a preferential circuit for use in an electronic musical instrument which is capable of producing in compliance with a predetermined priority order only a single musical tone corresponding to a certain key among keys which are held depressed simultaneously with each other.
2. Description of the Prior Art
An electronic musical instrument has generally an upper keyboard, lower keyboard and pedal keyboard used for producing melodious tones, chords and base tones respectively. These keyboards of a conventional type are arranged in such a manner that musical tones, which correspond to the respective keys of the keyboard held depressed simultaneously at a time, are produced together at the same time. The beginners for electronic musical instruments, however, commonly play melodious notes in sequence of independent musical notes, namely they play the notes one by one. Therefore, it is common for the known electronic musical instrument for beginners to have therein such a musical tone generating system for the upper keyboard as is implemented by employing a single tone configuration so as to simplify a circuit arrangement. The single tone configuration means that, when used in the musical tone generating system, only a single musical tone may be produced at a time which tone corresponds to a certain key among keys held depressed simultaneously with each other. In addition to the above, the electronic musical instrument manufactured exclusively for learning and teaching use may preferably be made by employing the single tone configuration in its musical tone generating system for an upper keyboard. Further in practice a musical tone generating system for a pedal keyboard has been generally implemented by using the single tone configuration.
For use in electronic musical instruments having the single tone configuration therein, there have been proposed a variety of circuit systems for a preferential circuit in which a musical tone corresponding to a certain key among keys held depressed simultaneously with each other is selectively determined in a predetermined priority order. One of the circuit systems is known as the high pitch preferential system in which a musical tone corresponding to a depressed key of a keyboard having a higher pitch is produced in preference to other tones of the keys being depressed. Another system is designated as the low pitch preferential system in which a musical tone corresponding to a key of a keyboard having a lower pitch is produced among the tones of the depressed keys. These two systems when applied to electronic musical instruments can make it possible to simplify circuit configuration on the one hand, and on the other hand, however, there is a disadvantage that the most appropriate musical note the player have in mind, which corresponds mostly to the newest depressed key, sometimes may fail to be produced at the time when the key is depressed. The other system is known as the last depression preferential system in which a musical tone corresponding to a key of a keyboard depressed last is produced in preference to the tones of other keys having been depressed. This system eliminates the disadvantages accompanying the above mentioned two circuit systems. The conventional last depression preferential system, however, has a disadvantage that, when a key is erroneously depressed after a correct key has been depressed, a relatively complicated operation is required to produce a correct musical tone by carrying out re-depression of the correct key after releasing it temporarily.